Polyunsaturated fatty acids (PUFA) represent an important component of animal and human nutrition. ω3 polyunsaturated fatty acids (also called n-3 polyunsaturated fatty acids) such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have a wide range of roles in many aspects of health, including brain development in children, eye functions, syntheses of hormones and other signaling substances, and prevention of cardiovascular disease, cancer, and diabetes mellitus (Non-Patent Documents 1 and 2). These fatty acids therefore represent an important component of human nutrition. Accordingly, there is a need for polyunsaturated fatty acid production.
Meanwhile, microorganisms of the class Labyrinthulomycetes are known to produce polyunsaturated fatty acids. Concerning microorganisms of the family Thraustochytrium, there are reports of, for example, a polyunsaturated fatty acid-containing phospholipid producing method using Schizochytrium microorganisms (Patent Document 1), and Thraustochytrium microorganisms having a docosahexaenoic acid producing ability (Patent Document 2). For enhancement of food and/or feed by the unsaturated fatty acids, there is a strong demand for a simple economical process for producing these unsaturated fatty acids, particularly in the eukaryotic system.
With regard to the class Labyrinthulomycetes, there have been reported foreign gene introducing methods for specific strains of the genus Schizochytrium (the genus Auranthiochytrium (Non-Patent Document 4) in the current classification scheme (Non-Patent Document 3)) (Patent Documents 3 and 4). Further, a method that causes a change in fatty acid composition by means of transformation is known in which a polyketide synthase (PKS) gene is destroyed to change the resulting fatty acid composition (Non-Patent Document 5). However, there is no report directed to changing a fatty acid composition by manipulating the enzymes of the elongase/desaturase pathway. Under these circumstances, the present inventors found ways to change fatty acid compositions through introduction of elongase/desaturase genes into various species of Labyrinthulomycetes, and have filed a patent application therefor (Patent Document 5).